Re: [PATCH #upstream-fixes] libata: clear PIO pad area

[Sergei Shtylyov <sshtylyov@mvista.com>]

Hello.

On 09/06/2011 08:58 PM, Tejun Heo wrote:

>>> ata_sff_data_xfer[32]() use pad area if the transfer size isn't
>>> multiple of transfer size; however, this area wasn't cleared and
>>> garbage data in pad area could be transferred to the device.  Make
>>> sure the pad area is cleared.

>>> Signed-off-by: Tejun Heo<tj@kernel.org>
>>> Cc: Lei Ming<tom.leiming@gmail.com>

>>     And what's the problem with garbage data? Why it's worse than 0s?

> There were devices which puke on random garbage at the end of CDB and

    Note that ATAPI CDBs are always aligned to 4 bytes, so this path should 
never be hit when sending them.

> in general sending indeterministic garbage to external device is a bad
> idea.  It increases chance of problems which can be difficult to
> reproduce and track down while gaining nothing.

    Problems with "don't care" padding bytes? Dunno...

> It really is a stupid thing to do.

    Well, at least the old code was equally stupid before I patched it. :-)

> Thanks.

WBR, Sergei